A numerical study of cylinders in waves and currents

The research on combination flow of planar oscillatory flow plus an in-line steady stream is of importance to the situation of structures in waves: an d current. The combination flow has not been studied extensively. There is still little information about the effect of current and about combined eff ect of current and waves on hydrodynamic loading of the structures. The pre sent study investigates the combination flow around a circular cylinder usi ng a vortex-based method incorporating vortex moving particles (discrete vo rtices) with a finite-difference scheme for the vorticity diffusion. The ma in attention is paid to the effects of a small current on in-line fluid for ces and vortex patterns in the wake. Morison's equation and an equation wit h two drag terms are examined. The results show that the presence of a smal l current in an oscillatory flow can reduce the drag coefficient significan tly. Morison's equation gives reasonably good predictions for the in-line f orces for an oscillatory flow plus a small current. The current tends to br ing the whole vortex wake downstream and tries to form the stable Karman as ymmetrical form in the downstream wake. The present results show certain ag reement with some previous experimental results. (C) 2000 Academic Press.